A new project!
I am always been fascinated by tube radio’s. They are made in a time when design, durability and quality counts compared to modern times. Also there are no better AM radio’s then these old tube radio’s because AM was mainstream in that time so manufactures did everything they can do to design a good sensitive receiver and audio circuit design.
I picked up this radio at a thrift shop. It is a 1958 Grundig 1070 FM, AM and LW radio. It was complete which is the most important thing when buying these old radio’s. Although it was complete it needed a lot of work because it had some defects:
- Only AM worked, but very low receiver sensitivity,
- Low amplifier power output with no bass at all,
- Electrostatic tweeter did not work,
- Cracked Bakelite case, and damaged paint,
- Dirty controls and switches,
- damaged power cord,
- Very dirty and dusty
How it came in:
look at the the burned main resistor:
Taking the chassis out of the cabinet:
Just a bit of dust:
Old paper wax capacitors. The radio is full of these Ero caps which became bad in all these years. They need to be replaced all to make the radio work again and prevent it from burning out the tubes caused by DC leakage through these capacitors:
The biggest problem with the radio was a broken power switch. It did not switched all the circuits on and off at the right moment. The cause of this was a broken piece of plastic which i managed to repair:
Then it was time for the electronics:
Measuring out the amplifier section. Everything was ok. The reason was a bad EL84 tube. So i replaced that one with a new one and that solved the weak audio and red plating of the tube.
Replaced the Selenium rectifier with a Silicium bridge rectifier:
Cleaned the scale background and the switches:
Replaced the paper caps:
New filter capacitors:
New B+ resistor replacing the burned red one:
some parts i replaced:
Then it was time to get the electrostatic tweeter working again:
The problem with these electrostats are the foam pads that dry out and crumble. When that happens they do not supply any pressure to the copper layer. Solution is to replace that piece of foam with a fresh new one. And that fixed it:
Repair the cracked cabinet:
Repainting the cabinet:
And finally it is ready!
Red plating EL84 tube: